Radiation therapy systems can be used to provide treatment to patients suffering a variety of conditions. Radiation therapy can be used to perform selective cell destruction, useful in controlling cancers by treating tumorous tissue. Particle therapy is a form of radiation therapy that uses light ions to destroy targeted cells. Particle therapy can be an efficacious way to selectively destroy targeted cells because light ions have unique dosimetric characteristics compared to other ionizing radiation, such as electrons or high energy photons. Light ions deposit most of their energy near the end of their path through a tissue. Because the dose provided by an ion is concentrated at a “Bragg peak” around the area where the ion stops, the dose to healthy tissue proximal to the target region may also be reduced. The well-defined maximum range of the ions ensures that tissue on the distal side of the target receives a negligible dose of radiation.
A particular type of particle therapy is proton therapy, in which the light ions species are protons. Protons are a convenient particle to use as they are the lightest ion species that provide the advantages described above.
One technique for delivering particle therapy is called pencil beam scanning. In this technique, the light ion beam remains narrowly collimated in a “pencil beam” and is steered in angle (deflection) and adjusted in range (energy) to deposit the dose as a small spot at a precise volume within the patient. Thus, complex volumetric shapes (e.g., organs) can be treated with a pencil beam without irradiating the surrounding tissue.
This approach is potentially very accurate. However, the small spot sizes can create the risk of uneven dose placement or “cold spots” should there be patient movement between exposures. In addition, precise measurement and control of the location and dosage (e.g., intensity distribution over time) of the spot is critical for safe and effective treatment of a patient.
Existing pixelated ionization detectors for measuring the location, transverse intensity distribution, and dosage of the beam spot typically have channel counts up to around 1,000. Such detectors either have low resolution over a large active area or high resolution over a small active area. While enhanced resolution at large area is possible, it can only be done at the cost increasing the number of readout electronic channels. This increases the cost of the device and requires an expensive high-capacity data link to transmit the large volume of data from the pixels to a receiving device at high update rates.
Accordingly, there is a need for a high-resolution detector that can accurately determine radiation dose and beam position over a large area using less expensive components while maintaining high update rates.